This invention relates to a rotating disk tracking system and more particularly, but not by way of limitation, to a multistage tracking system for an optical disk.
Heretofore, multistage tracking systems for an optical disk used a fine tracking element on a movable part such as a slow moving sled, i.e. laser vision or a bulky sled such as a gas laser based optical data recorder. When using a slow moving sled most of the work was done by the fine tracking element. The optical effects associated with large amplitude motion of the fine tracking element for instance vignetting, precludes positioning the mirror sled far from the objective lens. Therefore, it was found that the fine tracking element must be located on the sled. When using a small high performance system, it is an advantage to have a stationary fine tracking element because high speed access requires a lightweight high band width sled. This requires the sled to be capable of doing most of the work while tracking. The fine tracking element then will only have to move very slightly, thus avoiding the above-mentioned optical effects. If the fine tracking element is on the sled, this will contribute to the mass and complexity of the sled thereby reducing its response and consequently the element will have to do more of the work than in the previous situation.
The above-mentioned problems related to a multistage tracking system for an optical disk has led to invention as described herein. In the following U.S. patents, U.S. Pat. Nos. 4,225,873 to Winslow, Re. 29,963 to Janssen, and 3,829,622 to Elliot, optical systems are described having control systems with interacting loops and movable sleds with articulating mirrors thereon. None of these prior art patents particular point out the unique features and the advantages of the subject multistage tracking system as described herein.